Drop bogus debug assertion that we don't overpay on fees

We should always select at least as many coins as is required to
meet the feerate target, but its perfectly fine if we overshoot.
Specifically, we may overshoot deliberately if we choose to burn
change to fee instead.

Author: TheBlueMatt

lightning/src/events/bump_transaction.rs

@@ -703,11 +703,9 @@ where
 
 				let expected_package_fee = Amount::from_sat(fee_for_weight(package_target_feerate_sat_per_1000_weight,
 					signed_tx_weight + commitment_tx.weight().to_wu()));
-				// Our fee should be within a 5% error margin of the expected fee based on the
-				// feerate and transaction weight and we should never pay less than required.
-				let fee_error_margin = expected_package_fee * 5 / 100;
-				assert!(package_fee >= expected_package_fee &&
-					package_fee - fee_error_margin <= expected_package_fee);
+				// Our feerate should always be at least what we were seeking. It may overshoot if
+				// the coin selector burned funds to an OP_RETURN without a change output.
+				assert!(package_fee >= expected_package_fee);
 			}
 
 			log_info!(self.logger, "Broadcasting anchor transaction {} to bump channel close with txid {}",
@@ -811,11 +809,9 @@ where
 			let expected_signed_tx_fee = fee_for_weight(target_feerate_sat_per_1000_weight, signed_tx_weight);
 			let signed_tx_fee = total_input_amount -
 				htlc_tx.output.iter().map(|output| output.value.to_sat()).sum::<u64>();
-			// Our fee should be within a 5% error margin of the expected fee based on the
-			// feerate and transaction weight and we should never pay less than required.
-			let fee_error_margin = expected_signed_tx_fee * 5 / 100;
-			assert!(signed_tx_fee >= expected_signed_tx_fee &&
-				signed_tx_fee - fee_error_margin <= expected_signed_tx_fee);
+			// Our feerate should always be at least what we were seeking. It may overshoot if
+			// the coin selector burned funds to an OP_RETURN without a change output.
+			assert!(signed_tx_fee >= expected_signed_tx_fee);
 		}
 
 		log_info!(self.logger, "Broadcasting {}", log_tx!(htlc_tx));